1. Field of the Invention
The present invention relates to an improved corrosion inhibitor system and a method for using this corrosion inhibitor in gas wells. More specifically, it is concerned with an amine activated alkyl polysulfide oil optionally containing an oil-soluble corrosion inhibitor which is capable of maintaining a protective film at high temperature, high pressure bottomhole conditions in the absence of a petroleum condensate phase.
2. Description of Prior Art
The utilization of chemical corrosion inhibitors to protect metal surfaces in various stages of oil and gas production has long been recognized as a necessary feature of oil and gas production. During the past half century multitudes of chemical corrosion systems and methods of using them have been developed and have led to a vast number of patents and technical literature references. Thus, today, corrosion engineering is considered an integral part of the planning and operation of virtually every stage of oil and gas production.
With ever increasing world energy demands and the advent of international fuel shortages, the oil and gas industry has been forced to drill deeper and deeper into more hostile environments in search of the critically needed fuel. As a result, certain high temperature, high pressure deep horizon gas fields have been discovered throughout the world, which present a severe challenge to contemporary corrosion technology when one attempts to produce large volumes of natural gas from these fields.
The gas wells of particular interest in the present invention are characterized by a combination of properties that lead to corrosion rates many fold higher than experienced in other gas fields. First and foremost, the gas wells are completed at great depths which in many cases exceed 20,000 feet. Consequently, the gas wells are categorically high temperature, high pressure wells. As a general rule of thumb at bottomhole temperatures in excess of 250.degree. F. and bottomhole pressures of the order of about 4,000 psi, one can anticipate severe corrosion. As these bottomhole temperatures and pressures increase, the problem becomes even more pronounced such that at about 400.degree. F. and pressures in excess of 5,000 psi, the use of many corrosion inhibiting systems and methods is virtually prohibited. The gas wells of interest in the present invention are of this nature.
Furthermore, the particular gas wells of interest are dry wells in the sense that no liquid petroleum phase exists at the bottomhole conditions. Thus no protective oil film will be present to coat the casing and to act as a corrosion inhibitor carrier. In fact, since no condensate phase exists at these bottomhole conditions, injection of oil-soluble inhibitors in a petroleum condensate carrier will be ineffective because of premature vaporization of the carrier before reaching the bottom of the well.
To further complicate the lack of a petroleum condensate phase at the bottomhole conditions, the gas wells of interest will have an aqueous or brine phase present, and this, in combination with acid gases such as hydrogen sulfide, carbon dioxide or the like, create an extremely corrosive environment. With gas production in terms of tens of millions of standard cubic feet per day, the possibility of maintaining an oil condensate phase at bottomhole conditions is for all pragmatic purposes ruled out.
In an article entitled "Deep Wells--A Corrosion Engineering Challenge," by R. N. Tuttle and T. W. Hamby, presented at the International Corrosion Forum, Apr. 14-18, 1975, held at Toronto, Ontario, it was acknowledged that recent emphasis of deep high temperature, high pressure horizons as potential gas producers and the associated hostile environments encountered presents a severe challenge to contemporary technology. In the article it was pointed out that bottomhole temperatures as high as 550.degree. F. have been encountered in south Texas, and bottomhole pressures exceeding 22,000 psi are present in Mississippi. It was also pointed out that tubing failure caused by corrosion in deep wells has been experienced in as little as eight months in the Lacq Field in France, Germany, Austria, and also Mississippi. The Thomasville-Piney Woods Field near Jackson, Miss., is exemplified as involving gas wells that fit the above description and have severe corrosion problems. The False River field in Louisiana is believed to contain gas wells that would have bottomhole conditions characteristics of the present invention. The article concludes with an admission that a new corrosion inhibiting system to cover flowing conditions in the range of 18,000 to 20,000 psi and 380.degree. to 450.degree. F. is needed for completion of anticipated future wells in south Texas and Mississippi.